Our goal is to improve the clinical usefulness of glycoprotein markers of cancer (of which CEA is the prototype) by elucidating the key role of the liver in regulating levels of circulating glycoproteins and defining the mechanisms by which Kupffer and hepatic cells clear them. We seek a clinically useful means for reversibly inhibiting this clearance and raising levels. This will make possible earlier cancer detection as well as improved monitoring of treatment. Naturally occurring inhibitors of Kupffer cell CEA binding exist in some patients. We have studied patients with very high CEA levels (from 12,000 to over 200,000 ng/ml) and have shown that their CEA is cleared slowly by rat liver. In contrast to other CEAs, the CEAs of these patients tend to have approximately double the sialic acid content. An immunochemical test for the clinical detection of the highly sialated CEAs from these patients is being developed utilizing isoelectric focusing in agarose, electroblot transfer to nitrocellulose, and detection by specific antibody and immunoperoxidase staining. The presence of the markedly elevated CEA levels associated with slow CEA clearance has potential clinical use in earlier detection, diagnosis, prognosis, and response to therapy. A CEA-binding protein has been isolated from rat Kupffer cells. We have shown receptor-mediated endocytosis of CEA by rat alveolar macrophages in vitro. These alveolar cells bind CEA with the same specificity as Kupffer cells but with a more rapid rate of internalization. Since alveolar macrophages are easier to obtain then Kupffer cells, they may be useful for screening patients' blood for inhibitors of CEA endocytosis. A non-CEA marker for "undifferentiated" cancer is being sought using established colon cancer lines and a new undifferentiated colon cancer cell line (MIP101), which has been obtained from fresh biopsy tissue of a human colonic cancer and grown both in culture and in nude mice. The undifferentiated nature of MIP101 has been confirmed by ultrastructural analysis and is being further characterized. It produces no CEA and should prove useful in our search for an undifferentiated cancer marker. Monoclonal and polyclonal antibodies to the new putative tumor proteins are being screened using a battery of malignant tissues and cells in culture. (1)